The invention relates to a linear motion unit with a runner that is arranged so as to be movable back and forth along a rod, wherein there is provided in front of and/or behind the runner, in the runner""s direction of travel, at least one support unit that supports the rod relative to an essentially rigid counter-element. There is provided on the runner or a unit connected thereto a catch that can be brought into latched engagement with each support unit. The support unit comprises a base body that is longitudinally slidable relative to both the rod and the counter-element in the direction of motion yet is guided in a nonrotating manner with respect to the direction of travel, upon which base body is mounted a control member that can be moved between at least one latched position and at least one released position by means of a control track provided on the counter-element.
The aforementioned support units are usually used with linear motion units of this type in order to prevent sagging or bending of the rod when the length of the rod exceeds a maximum dimension that is a function of its diameter, its construction and the operating conditions to which it is subjected, among other factors. Naturally, the rod is subject to gravity regardless of the precise embodiment of the linear motion unit. In the case of linear drives in which the rotation of a rod embodied as a threaded spindle is translated into a linear motion of a runner including a threaded nut, there are also centrifugal forces acting on the threaded spindle that result from its rotation. Through the use of the support units mentioned, it is possible to keep the unsupported lengths of rod short enough that the sagging and/or bending of the rod between two adjacent support points does not exceed a tolerable amount.
Naturally, the support units must not hinder the movement of the runner. It must therefore be possible for the runner, as it moves in a given direction, to progressively xe2x80x9cpick upxe2x80x9d the support units located in front of it in its direction of motion. In addition, however, it must also be possible, after the runner reverses its direction of motion, for it to xe2x80x9cdrop offxe2x80x9d the previously collected support units at their intended support locations.
To this end, a type of linear drive has been proposed in EP 0 327 705 B1 in which the support units lock with the counter-element at their intended support positions. To this end, the support units are comprised of a base body that is in supportive engagement with both the rod, which is embodied as a threaded spindle, and the counter-element, which is embodied as a guide rail, and are also comprised of a control slide that is mounted in the base body so as to be movable orthogonally to the longitudinal direction of the threaded spindle. Here, the control slide is spring-preloaded with respect to the base body such that a latch provided on it is pressed against a slideway in which corresponding latch recesses are provided at the predefined support positions. In addition, a catch pin is arranged on the control slide. If the support unit is located in the region of a slide section of the slideway, the catch pin projects upward out of the support unit and engages a catch rail on the runner that carries the support unit along which the runner moves. In contrast, if the support unit is located in the region of a latch recess of the slideway, the latch falls into the latch recess as a result of the spring preloading of the control slide. The catch pin is thereby withdrawn from the catch rail of the runner, so that the latched engagement between the support unit and the catch rail is released.
A disadvantage of this solution is that when a plurality of support units are used, not only does the latch of the last support unit in the current direction of travel fall into the latch recess on the slideway provided for it, but in addition the latches of the support units arranged ahead of it do so as well when they pass by. Of course, the locking of those support units that have not yet reached their predefined positions is released by the support units that follow and are still in latched engagement with the catch rail. This ongoing latching and unlatching not only results in increased wear on the catches and latch recesses, but also leads to increased noise emission from the linear motion unit.
An object of the present invention is to provide a linear motion unit in accordance with the class that is distinguished by reduced wear and noise emission.
This object is attained in accordance with the invention by a linear motion unit of the aforementioned type in which the control element has at least one control recess extending essentially orthogonal to the direction of motion, and wherein the control track includes in at least one predetermined position a control projection that can be brought into engagement with the control recess and is arranged at an angle to the direction of motion so that, when the support unit moves, the control projection moves the control element essentially perpendicular to both the direction of motion and the direction of extension of the control recess. The primary difference with respect to the above-described solution per EP 0 327 705 B1 is that the direction of motion of the control element and the direction of extension of the control recess, in other words the latch recess in the case of EP 0 327 705 B1, are not essentially parallel to one another, but rather the motion of the control element resulting from engagement with the control projection is perpendicular to the direction of extension of the control recess of the control element. The control projection thus pushes the control element to the side, which only requires a low-noise and low-wear sliding engagement between the control projection and the parts of the control element surrounding the control recess.
It must be mentioned at this point that a xe2x80x9cmotion of the control element perpendicular to the direction of extensionxe2x80x9d must be understood to include not only an orthogonal motion of the control element essentially perpendicular to both the direction of extension and to the direction of motion, but also a circumferential motion about an axis essentially parallel to the direction of motion of the runner and/or the longitudinal axis of the rod.
Accordingly, the control element can be a control disk arranged to be rotatable on the base body about an axis essentially parallel to the longitudinal axis of the rod. However, it is also possible that the control element can be a control slide that is arranged to be movable on the base body in a direction essentially orthogonal to the longitudinal axis of the rod. In both embodiments, the control element can be held by a cover element in a recess formed between the cover element and a shoulder of the base body, which facilitates a simple design option for arranging the control element on the base body.
The latched engagement between the support unit and the runner and/or the unit attached thereto can be implemented in a simple fashion if the catch has a hook element. Moreover, an additional catch can be arranged on the base body to latch an adjacent support unit. This, as well, simplifies the design of the linear motion unit, because when a number of support units are used it is not necessary for all catches for these support units to be arranged on the runner, but instead each support unit can be brought into latched engagement with its neighboring support unit. The unit mentioned above in connection with the latched engagement that is attached to the runner can thus be a support unit that is in latched engagement with the runner, or a plurality of support units that are in latched engagement with one another and with the runner.
In order to establish and release the latched engagement, the hook element can interlock with a latch surface of the control element, and there can be provided in the latch surface at least one release recess that aligns with the hook element in the corresponding release position. Alternatively, it is also possible that the hook element interlocks with a latch surface of the base body and that the control element includes at least one cam that, in the corresponding release position, releases the engagement between the hook element and the base body.
In order to simplify the establishment of the latched engagement and/or ensure its establishment even in the case of a control element that is not adjusted precisely, it is proposed in a further refinement of the invention that the attachment of the hook element to the runner or to the unit attached thereto be accomplished by means of an arm, preferably elastic. If necessary, the latched engagement can thus be established by the locking of the hook element with the latch surface. To make this locking easier, provision can additionally be made for a guide bevel for facilitating the establishment of latched engagement to be formed on at least one of the two parts, i.e., that hook element and the control element or the hook element and the base body.
In order to be able to reliably hold the control element in the release position that at least some of the aforementioned embodiment variations require for the reestablishment of latched engagement, a safety device can be provided with a latching element, preferably spring-preloaded, that is arranged either on the base body or on the control element and that, in the release position, engages a latch recess in the other of the two parts, i.e., the control element or the base body, respectively. Alternatively, a frictionally-acting safety device can be provided, for example in the form of a brake device adjacent to the control projection that stands in braking engagement with the support unit, preferably the control member thereof. In this context, the brake device can be formed as a single piece on an angled section of the control rail. If the frictional forces already present between the control element and the base body of the support element are sufficient to prevent unintended movement of the control element, a separate safety device or brake device can be omitted altogether.
It is certainly possible for the control track arranged on the counter-element to comprise just the number of control projections required to move the control elements of the at least one support element. In order to always be able to ensure positive positioning of the control element, however, it is advantageous if the at least one control projection is part of a control rail that is arranged on the counter-element and is always engaged with at least one control recess of the control element, and preferably extends along the entire length of the rod. In this case, the control rail can have at least one straight longitudinal section and at least one angled longitudinal section, and is preferably composed of at least one straight longitudinal part and at least one angled longitudinal part. In this context, the straight section can have at least one guide projection that is arranged at essentially the same lateral position along the entire length of the straight section and is intended to engage an associated control recess, while the control projection of the angled section changes its lateral position along its length. Since the control element is thus switched along each of the angled sections in accordance with the invention, the release recess and/or the release cam also becomes aligned with the catch hook in the region of an angled section and releases the catch hook""s latched engagement with the latch surface. Thus, the angled sections define the positions at which the support units that are pulled along behind the runner as a result of their latched engagement are dropped off, i.e., the support positions.
It must also be mentioned that a damping device can be provided on at least one end face of the base body. This damping device can for example be comprised of a plurality of damping elements, preferably made of rubber or a rubber-like material. This damping device serves to dampen the impact, and in particular the noise, produced as the support units are xe2x80x9cpicked upxe2x80x9d by the runner.
The base body and/or the control element and/or the cover element and/or the elements of the control track can be made of plastic, which has a beneficial effect on the manufacturing costs of the linear motion unit in accordance with the invention.
The counter-element can be embodied as a rail, for example a guide rail for the runner, with a hollow profile open on at least one side, in whose interior space at least the rod and the at least one support unit are accommodated. This rail can, for example, be manufactured as an extruded aluminum profile.
In addition to the aforementioned possibility of embodying the linear motion unit as a roller spindle drive, the linear motion unit in accordance with the invention can also be used to advantage in other types of linear motion units. At this point, only linear bushing guides, magnetic piston units and linear motor modules will be mentioned. In magnetic piston units, the rod is implemented as a hollow tube in which a magnetic piston can be moved by the application of pressurized fluid, and the runner is coupled to the piston by magnetic forces. In linear motor modules, the rod is embodied as the push rod of a linear motor that drives the runner. The support is especially advantageous in this case, since forces of magnetic attraction between the rod and the counter-element act on the rod in addition to gravity. Since the use of support units in magnetic piston units and linear motor units was completely unknown, separate protection is sought for this concept.